GOP lawmakers have been loath to contradict the president publicly, but few are willing to embrace the conspiratorial claim, made in a series of tweets on Saturday morning. Trump has since demanded that Congress investigate the politically motivated surveillance that he believes occurred.

The White House insists Trump stands by the assertion, which FBI sources have denied to multiple media outlets, but officials are unable to say what basis he had for making it.

Unconfirmed media reports have indicated that people associated with Trump have been investigated for their ties to Russia, and wiretaps of foreign officials may have picked up their communications.

Circa reported Wednesday that the FBI obtained a legal FISA court warrant involving a computer server in Trump Tower that communicated with Russian banks, but no criminal activity was uncovered.

Sen. John Boozman, R-Ark., did not dismiss Trump’s allegation completely Wednesday, but he said in an interview with KATV that the intelligence agencies involved have provided nothing to support it.

“Right now, I don’t think there’s any evidence that the president of the United States did that, although there’s going to be a lot of investigation in that regard,” he said.

Boozman noted that presidents do not have the power to order such wiretaps, but the Department of Justice or the attorney general conceivably could.

Now that Trump has put the accusation out there, Sen. Richard Shelby, R-Ala., hopes Congress can find the truth.

“Whether they tapped President [Trump’s] headquarters or whatever was going on during the campaign, I don’t know that, but we ought to investigate,” Shelby said. “Maybe we’ll find the answer to it, maybe we won’t.”

Sen. Jim Risch, R-Idaho, a member of the Senate Intelligence Committee, declined to weigh in on Trump’s tweets.

“I don’t know anything about that,” he said. “I know exactly the same amount that you do. If there’s evidence that comes forth in that regard, I have no doubt that it will be very carefully weighed.”

Democrats have been more overtly skeptical of the president’s unsubstantiated charge.

“If the president has the facts or evidence, he should be turning that over to the committee,” said Jacky Rosen, D-Nev.

The House Intelligence Committee sent a request to FBI Director James Comey Wednesday for a briefing on several matters, including “the very serious allegations that the president and/or his associates were or are under surveillance.”

Sen. Lindsey Graham, R-S.C., told CNN he is prepared to subpoena intelligence agencies for any evidence of what Trump claimed. He and Sen. Sheldon Whitehouse, D-R.I., have sent Comey a letter seeking copies of any relevant warrant applications and court orders.

Heads of the House and Senate committees have indicated that the allegations will be part of their probes of alleged Russian interference with the election. Boozman said that scrutiny could be a good thing if it puts the questions Trump raised to rest.

“It’s complicated, but the good news is the president’s put it on the table and there’s going to be a lot of discussion about it,” he said.